Hitherto, active developments have been made on non-aqueous electrolytic secondary batteries using an alkali metal, for example lithium, sodium and the like, as a negative electrode, in which a positive active material is an interlayer compound, such as titanium disulfide, and an electrolyte is an organic one made by dissolving lithium perchlorate in an organic solvent such as propylene carbonate. The special features of these secondary batteries are high cell voltage and high energy density caused by using the alkali metal as the negative electrode.
However, the secondary batteries of this sort show short life of frequency (cycles) of charging and discharging when metallic lithium is used as the negative electrode. The charge and discharge efficiency also become low in making charge and discharge. It is believed that these defects are mostly brought about from a decline of the negative electrode. In other words, the lithium negative electrode is mainly prepared by attaching a lithium plate to a screen type current collecting substrate under pressure, and the electrode dissolves in the electrolyte as the lithium ion during discharging. However, it is difficult to change the dissolved lithium ion in the original lithium plate form as it was. The dissolved lithium ion may be actually deposited in a dendrite lithium form which easily breaks at the root and drops away, and it may also be deposited in a small spherical lithium which goes away from the current collecting substrate, which makes the battery impossible to charge and discharge. It may frequently happen that the dendrite lithium grows through a separator for dividing the positive and negative electrodes and connects with the positive electrode to result in short circuit which nullifies the function of the battery.
There have been proposed many improvements to overcome the above problems. Recently, the issue of charge and discharge efficiency of the negative electrode has considerably been improved due to the appearance of excellent lithium occluded alloys. It, in turn, has become more important to develop the materials having the excellent performance as positive active material rather than the negative electrode. As the positive electrode materials, a number of active materials have so far been proposed, among which for example titanium disulfide (TiS.sub.2), niobium selenide (NbSe.sub.2), vanadium oxides, such as V.sub.2 O.sub.5, V.sub.6 O.sub.13 and the like, tungsten oxide (WO.sub.3), molybdenum oxide (MoO.sub.3), chromium oxide (Cr.sub.3 O.sub.8), copper vanadate (Cu.sub.2 V.sub.2 O.sub.7), etc have been studied as positive active materials having high possibility. Generally, the performances required for the positive active materials to be used for the lithium secondary battery are the so-called high energy density with large electric capacity for discharge and high discharge voltage, voltage flatness thereof and cycle life. However, the above possible positive active materials do not entirely satisfy the above requirements. For example, TiS.sub.2 and NbSe.sub.2 show low discharge voltage, V.sub.2 O.sub.5 shows stepwise variation of voltage is discharge which exhibits no flatness, WO.sub.3 has small electric capacity, MoO.sub.3 shows low discharge voltage, Cr.sub.3 O.sub.8 provides a high voltage but has problems in its cycle life, and Cu.sub.2 V.sub.2 O.sub.7 involves a problem in cycle life. J. Electrochemical. Soc. vol. 128 No. 12 to K. M. Abraham, J. L. Goldman, and M. D. Dempsey 2493-2501 (1981) reports the result of studying oxides of Cr or V as a positive active material. The report by Abraham et al relates to V.sub.6 O.sub.13. V.sub.6 O.sub.13 is usually prepared by mixing V.sub.2 O.sub.5 and metallic vanadium and heating at 650.degree. C. The report by Abraham et al also considers Cr.sub.0.13 V.sub.0.87 O.sub.2.17 which is produced by using metallic chromium instead of metallic vanadium in the preparation process of V.sub.6 O.sub.13. In the above preparations, V and Cr is used as a reducing agent for changing V.sub.2 O.sub.5 to V.sub.6 O.sub.13 (VO.sub.2.17) and the product is Cr.sub.0.13 V.sub.0.87 O.sub.2.17 when Cr is employed, as mentioned before. It is also reported by Abraham et al that, when Cr.sub.0.13 V.sub.0.87 O.sub.2.17 is used as a positive active material to make a Li secondary battery, the cycle life becomes worse in comparison with V.sub.6 O.sub.13 (VO.sub.2.17) and the discharge voltage is also low. This is believed to arise from the fact that the oxide is prepared from V.sub.2 O.sub.5 and metallic chromium.
The discharge voltage of the oxides generally is higher in the case of high oxidation number than in the case of low oxidation number. When comparing V.sub.2 O.sub.5 (the oxidation number of vanadium equals five) with V.sub.6 O.sub.13 (the oxidation number of vanadium equals 4.34), V.sub.2 O.sub.5 has higher discharge voltage and the difference thereof is about 0.4 volt.
The average oxidation number per one metal ion in Cr.sub.0.13 V.sub.0.87 O.sub.2.17 is 4.34 and its discharge voltage has similar value to V.sub.6 O.sub.13. Accordingly, cycle life and discharge voltage are better in V.sub.2 O.sub.5. However, even V.sub.2 O.sub.5 shows low discharge voltage and stepwise variation of voltage in discharging.
As mentioned above, there has been no materials of practical utility as a positive electrode material for the secondary battery using non-aqueous electrolyte. Accordingly, appearance of the positive active material having high voltage, good voltage flatness in discharging, large electric capacity and long cycle life is desired.